If you can get away without using corrugated and just use board stock (think cereal boxes) this will give you more options.

Most short run corrugated is typically silk screen. They charge per color on silk screening. Board stock can be run on some digital presses, such as Xerox iGen or HP Indigo's. Unlike silk screen, digital presses are either black or 4 color process (full color) This will give your designer more options when it comes to designing that packaging.

Do a search on "short run packaging printing" this should get you pointed in the right direction.

I was in the printing industry for 12 years, so if you have any questions please feel free to PM and I will try to help.

Yes alibaba is pretty good for that(choose a supplier with at least escrow system+ 2yr gold supplier)
I've ever ordered some boxes by one of the seller and my sample at the start was 250$ but after 5 to 10 mail the sample cost me 55$.
The same 55$ were substracted from the final order.
Before to order a sample, give all details to the seller :
psd/jpg/pdf/... files, thick of the box, surface disposal,...

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